DIO6905C

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DIO6905C • Rev. 1.1

- 12 -

Selecting the output capacitor

The output capacitor (C2) stabilizes the DC output voltage. Ceramic capacitors are recommended. Use low ESR

capacitors to limit the output voltage ripple. Estimate the output voltage ripple with Equation (8):

)

2

*

f

*

8

1

(

*

)

1

(

*

*

f

1

S

C

R

V

V

L

V

V

S

ESR

IN

OUT

OUT

OUT







△

(8)

Where L1 is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor.

When using ceramic capacitors, the capacitance dominates the impedance at the switching frequency, and

causes most of the output voltage ripple. For simplification, the output voltage ripple can be estimated with

Equation (9):

)

1

(

*

2

*

*

f

*

8

1

2

S

IN

OUT

OUT

OUT

V

V

C

L

V

V





△

(9)

For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For

simplification, the output ripple can be approximated with Equation (10):

ESR

IN

OUT

OUT

OUT

R

V

V

L

V

V

*

)

1

(

*

*

f

1

S





△

(10)

The characteristics of the output capacitor also affect the stability of the regulation system.